Wdm layer-based optical chanel protecting device and method thereof

ABSTRACT

The present invention discloses a WDM layer-based OChP device and the method thereof, i.e., M protection channels are added in the transmitting module and the receiving module to connect to receiving ends and transmitting ends of M protection channels in the WDM system; a switching device is added so as to switch signals in specified working channels to specified protection channels or switch signals transmitted in specified protection channels back to specified working channels according to switching requests from the WDM system; wherein M and N are natural numbers, and M&lt;N. Because the number M of protection channels is less than the number N of the working channels, compared with 1+1 or 1:1 protection solution, this solution helps to save optical wavelength resource and initial cost. In addition, compared with 1+1 or 1:1 protection solution, when M&gt;1, this solution can significantly reduce the risk of ruined backup performance due to above failures, without requiring increased cost.

FIELD OF THE INVENTION

The present invention relates to a WDM layer-based Optical ChannelProtection (OChP) device and method thereof.

BACKGROUND OF THE INVENTION

As Dense Wavelength Division Multiplex (DWDM) technology evolvesrapidly, the transmission rate of WDM system increases quickly to meetever-growing network data service and voice/image service requirementsas well as telecom operators' ever-increasing demand for highertransmission bandwidth; at the same time, the reliability of WDM systembecomes a prominent issue. On the basis of enhanced reliability ofsystem modules, implementing a good protection solution will bringsignificant benefit to system reliability.

Presently, there are two types of WDM system protection solutions: oneis Optical Multiplex Segment Protection (OMSP), which is also referredto as optical line protection; the other is OChP; the object of theformer is primarily to protect transmission optical fibers; while thelatter provides equipment-level protection and it employs the followingworking principle: whenever the signal transmission in a channel isinterrupted or the performance is degraded to a certain degree, theswitching device of the system will switch the signals from the channelto a protection channel to transmit; whether to perform the switch issolely determined by the determination device in the receiver accordingto the quality of received signals and requires no additional detectiondevice.

As DWDM technology evolves by leaps and bounds and the transmission rateincreases in doubles, the traffic in each channel becomes increasinglyheavier, and the role of transmission channels in the network becomesmore significant; as a result, the security and reliability of eachchannel becomes an inevitable factor in the network, which requiresbetter OChP solutions.

One of the common OChP solutions for traditional WDM systems employs 1+1or 1:1 scheme (where 1+1 represents cold backup; 1:1 represents hotbackup; the difference between them lies in whether the protectionchannel transfers traffic when the working channel operates normally),i.e., a power distribution device is added at the optical signal inputend of each working Optical Transform Unit (OTU), and one of the twosignal outputs of the power distribution device is connected to theworking OTU, the other signal output is connected to a backup OTU; inthis way, in case the working OTU fails, the input signals may bechanged to the backup OTU so as to ensure normal operation of thesystem. A typical 1+1 solution is shown in FIG. 1. And the coupler shownin FIG. 1 may be substituted with a 1×2 optical switch. The solid lineportion in FIG. 1 shows routes of working channels, and the dotted lineportion shows routes of protection channels. The feature of such aprotection solution is that it utilizes a wavelength signal to protectanother wavelength signal; therefore the number of working channels isequal to that of protection channels. Though above WDM-based 1+1 OChPsolution can solve the problem of channel reliability, it requireshigher initial cost of equipment because half of the wavelength resourceis wasted.

SUMMARY OF THE INVENTION

The object of the present invention is to solve the above problem and toprovide a WDM layer-based OChP device and method thereof, so as torealize an independent protection mechanism for the WDM layer withreduced wavelength waste and initial cost of equipment.

To attain said object, the present invention provides a WDM layer-basedOChP device and a method thereof, so as to achieve signal transmissionfor working channels and routing selection for protection channelsbetween the traffic transferred and the WDM system.

Said OChP device comprises a transmitting module and a receiving module;said transmitting module and receiving module both comprise N workingchannels connected to the receiving ends and transmitting ends of Nworking channels in the WDM system respectively, wherein saidtransmitting module and receiving module also comprise M protectionchannels, which are connected to the receiving ends and transmittingends of M protection channels in the WDM system, and a switching device,which is designed to switch the signals in specified working channels tospecified protection channels or switch the signals in specifiedprotection channels back to specified working channels according to theswitching requests from the WDM system; wherein M and N are both naturalnumbers, and M<N.

Said OChP method comprises the following steps:

-   -   (1) The WDM system monitoring the quality of signals in each        channel and routing state of OChP modules in the system in real        time;    -   (2) The WDM system determining whether there are some signals in        the working channels should be switched to the protection        channels; if yes, the WDM system selecting the protection        channels;    -   (3) The WDM system sending accurate switching requests to the        OChP transmitting module and the OChP receiving module;    -   (4) The OChP transmitting module and the OChP receiving module        performing switch according to said switching requests from the        WDM system.

With above solution, in normal cases, the OChP module choosescorresponding working channels for N-way signals entering said OChPmodule to access the WDM system to transmit; at the receiving end, theOChP module similarly chooses working channels to receive the signals;at this time, no traffic is transmitted in the protection channels, orthe traffic transmitted through the protection channels will not bereceived by the OChP receiving module (only the traffic with lowpriority is transmitted). In case the quality of signals in m channels(1≦m≦M) is degraded or lost due to channel failure, the OChP module atthe transmitting end will switch the signals to protection channels totransmit; while the rest N-m signals are transmitted through the workingchannels; at the receiving end, the OChP module chooses correspondingprotection channels to receive said m signals, and the rest N-m signalsare received by the working channels. In this way, a WDM layer-based M:NOChP solution is implemented. Due to the fact that the number ofchannels and the probability of degraded signals or lost signals aretrivial, the number M of protection channels may be less than the numberN of working channels. Compared with 1+1 protection solution, it helpsto save resource and initial cost. In case the number M of protectionchannels is more than 1, there are two or more cascade backup OTUs,which further reduces the risk of ruined backup performance due tofailures of backup OTUs or failures of two or more working OTUs, withoutincreasing construction cost of the system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a traditional WDM-based 1+1 OChPsolution.

FIG. 2 a shows the positions of the OChP modules in the WDM systemaccording to the present invention.

FIG. 2 b is a schematic diagram of a WDM-based 1+N OChP solutionaccording to the present invention.

FIG. 3 shows the internal structure of an OChP module composed ofcouplers and optical switches.

FIG. 4 shows the internal structure of the OChP module composed ofoptical switches.

FIG. 5 shows the structure of an OChP module composed of N×(N+M) opticalswitches.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will be described in further detail with referenceto the following embodiments and drawings. The embodiments are suitablefor both hot backup (M:N) and cold backup (M+N).

Referring to FIG. 2 a, the WDM layer-based OChP device according to thepresent invention comprises a transmitting module and a receivingmodule; said transmitting module and receiving module both comprise Nworking channels (N inputs and N outputs) connected to the receivingends and transmitting ends of N working channels in the WDM systemrespectively.

Said transmitting module and receiving module also comprise M protectionchannels connected to the receiving ends and transmitting ends of Mprotection channels in the WDM system respectively.

Said transmitting module and receiving module also comprise a switchingdevice, which is designed to switch the signals in specified workingchannels to specified protection channels or switch the signals inspecified protection channels back to specified working channelsaccording to the switching requests from the WDM system; wherein M and Nare both natural numbers, and M<N. Referring to FIG. 2 b (when M=1),compared with 1+1 protection solution, it helps to save resource andinitial cost by using only one protection channel to protect the workingchannels.

Though the 1:N or 1+1 protection solution shown in FIG. 2 b can help toreduce the number of backup OTUs in use and enhance utilization ratio ofoptical wavelength, the premise for it is that the OTUs should operatenormally; and if a backup OTU goes into a “trouble” state or OTUs in twoor more working channels protected by the same backup OTU goes into a“trouble” state, the backup performance of the system is ruined. Thesolution is to have more than one protection channels, as shown in FIG.3, FIG. 4, and FIG. 5.

Said device works as follows: in normal cases, the OChP module choosescorresponding working channels for N-way signals entering said OChPmodule to access the WDM system to transmit; at the receiving end, theOChP module similarly chooses working channels to receive the signals;at this time, no traffic is transmitted in the protection channels, orthe traffic transmitted through the protection channels will not bereceived by the OChP receiving module. In case the quality of signals inm channels (1≦m≦M) is degraded or lost due to channel failure, the OChPtransmitting module switches the signals to protection channels totransmit; while the rest N-m signals are transmitted through the workingchannels; at the receiving end, the OChP module chooses correspondingprotection channels to receive said m signals, and the rest N-m signalsare received by the working channels. If a working channel for a signalcurrently transmitted through the protection channel recovers, the OChPmodule switches the signal back to the working channel.

Here, whether the signal in a working channel is switched to aprotection channel is determined by the performance of the workingchannel and is solely determined by the corresponding receiver in theWDM system without any additional detection device because all receiversin the WDM system possess the function. In addition, whether the signalstransmitted through a protection channel are switched back to theworking channel also is determined by the performance of the workingchannel; therefore, the protection solution is WDM layer-based.

Both for working channels and protection channels, the OChP modules onlychoose corresponding routes for the signals instead of performing anytreatment to the traffic carried by the signals; therefore, the OChPmodules are transparent to the traffic.

Because the selection of routes of the signals performed by OChP modulesis based on the performance of channels in the WDM system, it requiressupport from an appropriate protocol between the WDM system and the OChPmodules. The protocol shall support the following functions:

-   -   (1) The WDM system monitoring the quality of signals in each        channel and routing state of OChP modules in the system in real        time;    -   (2) The WDM system determining whether some signals in the        working channels should be switched to the protection channels        and selecting the protection channels; similarly, the WDM system        determining whether there are some signals in the protection        channels should be switched back to the working channels;    -   (3) The WDM system sending accurate switching requests to the        OChP transmitting module and the OChP receiving module        simultaneously;    -   (4) The OChP modules performing switching according to said        switching requests from the WDM system.

In view of above required features of OChP modules, we implemented thedesign. And the typical embodiments are described as follows:

Embodiment 1

The OChP modules comprise 50:50 couplers (also referred to as shunts)and M:N (or M×N or N×M, indicating M or N input ports and N or M outputports) optical switches; Referring to FIG. 3, the switching device ofthe transmitting module comprises N 50:50 couplers and an N×M opticalswitch; one of the two output ports of each coupler is connected to aworking channel, and the other is connected to an input port of the N×Moptical switch; M output ports of the N×M optical switch are connectedto the M protection channels in the WDM system respectively; theswitching device of the receiving module comprises 50:50 couplers and anM×N optical switch, one of the two input ports of each coupler isconnected to a working channel in the WDM system, and the other isconnected to an output port of the N×M optical switch; M input ports ofthe M×N optical switch are connected to the M protection channels in theWDM system respectively.

In the above case, the M:N optical switch should be controlled so thatthe lasers for working channels and protection channels at receiving endof the WDM system are not open simultaneously; instead, only either ofthem can be in working state; however, no such requirement is necessaryfor the lasers at transmitting end.

Embodiment 2

The OChP modules comprise 1×2 optical switches and M:N optical switches.Referring to FIG. 4, the switching device of the transmitting modulecomprises N 1×2 optical switches and an N×M optical switch; one of thetwo output ports of each 1×2 optical switch is connected to a workingchannel in the WDM system, the other is connected to an input port ofthe N×M optical switch; and M output ports of the N×M optical switch areconnected to M protection channels in the WDM system respectively. Theswitching device of the receiving module comprises N 1×2 opticalswitches and a M×N optical switch; one of the two input ports of each1×2 optical switch is connected to a working channel in the WDM system,the other is connected to an output port of the N×M optical switch; andM input ports of the M×N optical switch are connected to M protectionchannels in the WDM system respectively.

The above solution requires strict protocol control for the M:N opticalswitch and the 1×2 optical switches, i.e., the optical switches at bothends shall be switched to corresponding routes simultaneously; however,no such requirement is necessary for the lasers at transmitting end andreceiving end.

Embodiment 3

The OChP modules comprise N×(N+M) optical switches. Referring to FIG. 5,the switching device of the transmitting module comprises an N×(N+M)optical switch, the N+M output ports of which are connected to N workingchannels and M protection channels in the WDM system respectively; theswitching device of the receiving module comprises a (N+M)×N opticalswitch, the N+M input ports of which are connected to N working channelsand M protection channels in the WDM system.

The above solution requires that the optical switches at both ends beswitched to corresponding routes simultaneously; however, no suchrequirement is necessary for the lasers at transmitting end andreceiving end.

The following calculation shows that the reliability of the system canbe enhanced when M>1.

For any of above embodiments, for 2+16 wavelength protection (equivalentto two cascaded OTUs, i.e., two independent 1+8 protection devices arecascaded to form a 2+16 protection device), according to thecalculation, the Mean Time Between Failures (MTBF) is prolonged by k/30times (compared with original solution of two independent 1+8 protectiondevices), where k is the ratio of system available time to Time BetweenFailures (TBF). For example, if the availability of a single board is99.99%, the value of k is about 10⁴; whenever a 9 is added after thedecimal fraction part of the value of the availability, the value of kgrows by an order of magnitude. If M+N solution (i.e., M cascaded OTUs)is used, the MTBF is prolonged by k^(M−1)P₈ ²/P_(8M) ^(M+1) times (Prepresents factorial function). It is obvious that the OChP methodaccording to the present invention helps to reduce cost and enhancesystem reliability when M>1.

1. A WDM layer-based OchP (Optical Channel Protection) device capable ofsignal transmission on working channels and routing selection forprotection channels between the transferred traffic and the WDM system,comprising a transmitting module and a receiving module; thetransmitting module and the receiving module each comprising N workingchannels connected to receiving ends and to transmitting ends of Nworking channels of the WDM system respectively, M protection channelsconnected to receiving ends and to transmitting ends of M protectionchannels in the WDM system respectively; and a switching device designedto switch signals in the working channels to the protection channels andto switch signals in the protection channels to the working channelsaccording to switching requests from the WDM system; wherein M and N arenatural numbers and M<N.
 2. The WDM layer-based OChP device according toclaim 1, wherein M is greater than
 1. 3. The WDM layer-based OChP deviceaccording to claim 1, wherein the switching device of the transmittingmodule comprises N 50:50 couplers and an N×M optical switch; one of thetwo output ports of each coupler being connected to a working channel inthe WDM system, the other of the two output ports being connected to aninput port of the N×M optical switch; M output ports of the N×M opticalswitch being connected to the M protection channels of the WDM systemrespectively; and wherein the switching device of the receiving modulecomprises N 50:50 couplers and an M×N optical switch, one of the twoinput ports of each coupler being connected to a working channel in theWDM system, and the other of the two input ports being connected to anoutput port of the M×N optical switch; M input ports of the M×N opticalswitch being connected to the M protection channels of the WDM systemrespectively.
 4. The WDM layer-based OChP device according to claim 1,wherein the switching device of the transmitting module comprises N 1×2optical switches and an N×M optical switch, one of the two output portsof each 1×2 optical switch being connected to a working channel in theWDM system, the other of the two output ports being connected to aninput port of the N×M optical switch; M output ports of the N×M opticalswitch being connected to the M protection channels of the WDM systemrespectively; and wherein the switching device of the receiving modulecomprises N 1×2 optical switches and an M×N optical switch, one of thetwo input ports of each 1×2 optical switch being connected to a workingchannel in the WDM system, the other of the two input ports beingconnected to an output port of the M×N optical switch, and M input portsof the M×N optical switch being connected to the M protection channelsof the WDM system respectively.
 5. The WDM layer-based OChP deviceaccording to claim 1, wherein said switching device of said transmittingmodule comprises an N×(N+M) optical switch, the N+M output ports of theN×(N+M) optical switch being connected to the N working channels and theM protection channels of the WDM system respectively; and wherein theswitching device of the receiving module comprises an (N+M)×N opticalswitch, the N+M input ports of the (N+M)×N optical switch beingconnected to the N working channels and the M protection channels of theWDM system respectively.
 6. A WDM layer-based OChP method capable ofsignal transmission through working channels and routing selection forprotection channels between the transferred traffic and the WDM systemcomprising the following steps: monitoring by the WDM system of qualityof signals in each channel and routing state of OchP modules in thesystem in real time; determining by the WDM system whether some signalsin the working channels are to be switched to the protection channels;and if they are, selecting the protection channels the WDM system;sending by the WDM system of accurate switching requests to the OchPtransmitting module and the OchP receiving module; performing by theOchP transmitting module and the OchP receiving module of switchingaccording to the switching requests from the WDM system; wherein the WDMsystem comprises N working channels and M protection channels, M and Nbeing natural numbers, M being less than N.
 7. The WDM layer-based OchPmethod according to claim 6, wherein M is greater than
 1. 8. The WDMlayer-based OchP method according to claim 6, further comprisingdetermining by the WDM system whether come signals transmitted in theprotection channels are to be switched back to the working channels, andif they are, determining the working channel to receive the signals, andsending accurate switching requests to the OchP transmitting module andthe OchP receiving module simultaneously.
 9. The WDM layer-based OChPmethod according to claim 6, wherein when no signals are switched to theprotection channels, the protection channels carry traffic with lowpriority.
 10. A WDM layer-based optical channel protection device for amulti-channel WDM system comprising a transmitter comprising Ntransmitter inputs; N working outputs, each working output beingconnected to the receiving end of a working channel of the WDM system; Mprotection outputs, each protection output being connected to thereceiving end of a protection channel of the WDM system; and atransmitter switching unit capable of directing signals from the Nsignal inputs to the N working outputs and to the M protection outputs;and a receiver comprising N receiver outputs; N working inputs, eachworking input being connected to the transmitting end of a workingchannel of the WDM system; M protection inputs, each protection inputbeing connected to the transmitting end of a protection channel of theWDM system; and a receiver switching unit capable of directing signalsto the N signal outputs from the N working inputs and from the Mprotection inputs; wherein M is less than N.
 11. The device of claim 10,wherein M is greater than
 1. 12. The device of claim 10, wherein thetransmitter switching unit comprises an N×M transmitter optical switchcomprising N input ports and M output ports, each output port beingcoupled to the receiving end of a protection channel of the WDM systemand N transmitter couplers, each transmitter coupler comprising an inputport coupled to a corresponding transmitter input, a first output portcoupled to the receiving end of a working channel of the WDM system, anda second output port coupled to an input port of the N×M transmitteroptical switch; and wherein the receiver switching unit comprises an M×Nreceiver optical switch comprising M input ports and N output ports,each input port being coupled to the transmitting end of a protectionchannel of the WDM system and N receiver couplers, each receiver couplercomprising an output port coupled to a corresponding receiver output, afirst input port coupled to the transmitting end of a working channel ofthe WDM system, and a second input port coupled to an output port of theM×N receiver optical switch.
 13. The device of claim 10, wherein thetransmitter switching unit comprises an N×M transmitter optical switchcomprising N input ports and M output ports, each output port beingcoupled to the receiving end of a protection channel of the WDM systemand N transmitter 1×2 optical switches, each transmitter 1×2 opticalswitch comprising an input port coupled to a corresponding transmitterinput, a first output port coupled to the receiving end of a workingchannel of the WDM system, and a second output port coupled to an inputport of the N×M transmitter optical switch; and wherein the receiverswitching unit comprises an M×N receiver optical switch comprising Minput ports and N output ports, each input port being coupled to thetransmitting end of a protection channel of the WDM system and Nreceiver 1×2 optical switches, each receiver 1×2 optical switchcomprising an output port coupled to a corresponding receiver output, afirst input port coupled to the transmitting end of a working channel ofthe WDM system, and a second input port coupled to an output port of theM×N receiver optical switch.
 14. The device of claim 10, wherein thetransmitter switching unit comprises an N×(N+M) transmitter opticalswitch comprising N input ports, each input port being coupled to acorresponding transmitter input, N output ports, each of the N outputports being coupled to the receiving end of a working channel of the WDMsystem, and M output ports, each of the M output ports being coupled tothe receiving end of a protection channel of the WDM system and whereinthe receiver switching unit comprises an (N+M)×N receiver optical switchcomprising N output ports, each output port being coupled to acorresponding receiver output, N input ports, each of the N input portsbeing coupled to the transmitting end of a working channel of the WDMsystem, and M input ports, each of the M input ports being coupled tothe transmitting end of a protection channel of the WDM system.
 15. AWDM layer-based optical channel protection method for a multi-channelWDM system comprising monitoring quality of signals carried by thechannels, determining based on the quality of a signal in a workingchannel whether to route the signal via a protection channel, sending afirst switching request to a transmitter switching unit to route thesignal via a protection channel, and sending a second switching requestto a receiver switching unit to route the signal via a protectionchannel, wherein the multi-channel WDM system comprises N workingchannels and M protection channels, M being less than N.
 16. The methodof claim 15, wherein M is greater than
 1. 17. The method of claim 15,further comprising determining whether to route a signal on a protectionchannel via the signal's working channel; sending a first switchingrequest to a transmitter switching unit to route the signal via thesignal's working channel, and sending a second switching request to areceiver switching unit to route the signal via the signal's workingchannel.
 18. The method of claim 15, further comprising routinglow-priority traffic via the protection channels when the protectionchannels do not carry signals.